Gas discharge display panels having conditioning cells

ABSTRACT

A display system utilising gas discharge display panels, with or without a matrix delimiting the display cells, wherein the panel is conditioned by &#39;&#39;&#39;&#39;internal optical&#39;&#39;&#39;&#39; conditioning, to permit the display cells to develop a very fast response. For this purpose, cells distributed over the whole of the surface of the panel are reserved for conditioning and are &#39;&#39;&#39;&#39;illuminated&#39;&#39;&#39;&#39; at a frequency sufficiently lower than the holding frequency of the display cells, not to disturb the observation.

United States Patent [191 Reboul et al.

[ Aug. 27, 1974 GAS DISCHARGE DISPLAY PANELS HAVING CONDITIONING CELLS Jean Phillippe Reboul; Jacques Portmann, both of Paris, France Thomson-CSF, Paris, France Dec. 19, 1972 lnventors:

Assignee:

Filed:

Appl. No.:

Foreign Application Priority Data Dec. 23, 197] France 71.46397 US. Cl 340/324 M, 315/169 TV, 340/336, 340/343 Int. Cl. G091 9/32 Field of Search 340/324 M, 343, 173 PL, 340/324 R, 336; 315/169 TV References Cited UNITED STATES PATENTS 4/1970 Holz 315/169 TV 3,644,925 2/1972 Kupsky....; 340/324 M Primary Examiner-John W. Caldwell Assistant ExaminerMarshall M. Curtis Attorney, Agent, or FirmRoland Plottel, Esq.

[57] ABSTRACT 4 Clains, 2 Drawing Figures l GAS DISCHARGE DISPLAY PANELS HAVING CONDITIONING CELLS The present invention relates to improvements in display systems employing display panels of the gasdischarge kind, which improvements in particular make it possible to improve the rapidity of their response to writing signals, that is to reduce the time lag extending between the application of a control signal to the panel and the effect produced by this signal, in other words the display.

Gas-discharges display panels are now well-known and require no further detailed description here. A relatively detailed description is, however, given in US. Pat. application Ser. No. 302,413, and assign to the same assignee as the present application, and entitled: An improved method of controlling a gas-discharge display panel, and the display systems employing such a method.

Suffice it to recapitulate here that such display panels are generally constituted by a network of cells filled with a gas or gas mixture, the ionization of which is controlled by signals applied to an intercrossing network of electrodes. In some embodiments, these cells are materially delimited and separated from one another; such embodiments comprise insulating matrices provided with gas filled holes, the control electrodes,

separating the cell from the electrode network, electrical charges which create a storage voltage between said walls and thus stop the ionisation. The thus activated or written cell, i.e., having a storage voltage, is then subjected to an alternating electric field produced by a holding signal applied to the panel assembly, which field is insufficiently strong to ionise the unwritten cells but sufficiently strong to ionise the written cells which then briefly light up twice per cycle of the holding signal.

A major and delicate problem which has to be resolved in this context is that of the conditioning" of these panels. In other words, rapid response by a panel to a writing signal, is only possible if the ionization of the cells to be recorded takes place as soon as the writing signal is applied. For this to happen, it is necessary that the gas shall contain a sufficient number of free electrons to produce rapid electron avalanche and therefore ionisation. If no particular precaution is taken to ensure that the panel permanently has such free electrons, these being known as conditioning electrons, then in the response of the cells a lag time occurs which may be as much as several seconds and thus considerably limits the field of application of the panel.

At the present date, several methods of contioning are known.

One simple method consists in distributing within the gas a small dose of a radioactive product which slightly ionizes the gas and thus creates conditioning electrons.

2 However, for large-sized panels, this process is impracticable because it would lead to a level of radioactivity exceeding the permissible limit.

Another method used is an electrical conditioning which consists in ionising the set of cells at a frequency very much lower than that of the holding signal, whilst arranging that after this ionisation they retain the state which they had before (i.e., written cell or not written cell). Unfortunately, such a method is difficult to be correctly carried out and disturbances may appear in the display.

Optical conditioning methods are also known in which the conditioning electrons are photo-electrons produced in the gas by a light source, which may be outside the panel, but which then disturbs its observation, or by permanent illumination of the peripheral cells of the panel. This permanent illumination, excludes certain types of control. Moreover, conditioning is only properly effected for panels without matrices. The ultravioled rays produced by the luminescence of the peripheral cells would be very highly attenuated by a matrix and would quickly become inadequate to produce photoelectrons in cells at any distance from the periphery.

The present invention is concerned with gas discharge display panels with or without matrix, in which the conditioning is effected in an efficient manner by a special optical method.

In the panel systems in accordance with the invention, a certain number of cells distributed over the whole of the surface of the panel are reserved exclusively for the conditioning function; the electrodes which control them are supplied permanently and solely with signals having a sufficient amplitude to briefly ionise these cells at a frequency much lower than the frequency of the holding signal applied to the other cells of the panel, in order not to disturb the display.

The number of cells reserved for the conditioning operation, and their distribution within the panel, depend upon the type of information to be displayed and are based upon a compromisebetween adequate conditioning to permit rapid display but at the same time not too important to not disturb the observation of the display, the cells thus used for the conditioning function not being usable for the display function.

According the present invention'there is provided a display system with a gas discharge display panel, comprising a network of cells filled with gas ionizable on application of signals of appropriate amplitude between electrodes for controlling said cells, said control electrodes constituting a network of intercrossing electrodes disposed in lines and columns, an alternating holding signal of periodicity T being applied between the control electrodes of the cells used for display, and producing, twice per cycle T the ionisation of. the written cells, that is to say the cells already ionised by the application of a writing control signal and a conditioning of the panel being realised for providing within said panel some free electrons, said contioning being realised by means of certain predetermined cells known as conditioning cells, distributed over the whole of the surface of the panel and being utilised only for said conditioning function, signals of an amplitude high enough to provoke ionisation of said conditioning cells being provided between the electrodes controlling them at a frequency n times higher than the frequency l/T of said holding signal.

Other objects, features and results of the invention will become apparent from the ensuing description, given by way of non-limitative example and illustrated by the attached figures in which:

FIG. 1 illustrates graphs showing theform of different signals applied to the panels of the systems in accordance with the invention;

FIG. 2 illustrates a partial, schematic view of an embodiment of a system in accordance with the invention.

In the display systems in accordance with the invention, as already briefly mentioned hereinbefore, cells distributed over the whole of the surface of the display panel are reserved exclusively for the conditioning function. For this purpose, a certain number of electrodes of the intercrossed network, that is to say a certain number of line and column electrodes, are not supplied with any of the display control signals proper (holding signals, writing signals, erase signals. but only with conditioning signals in accordance with the invention.

The choice of these electrodes is made in such a way that the optical conditioning that they permit acts upon all the display cells, that is to say that the islands of display cells which they delimit, do not have excessively large dimensions. Moreover, theirv distribution and number are a function of the kind of data to be displayed: curves, graphs or alphanumerical characters.

Examples have been given of this hereinafter,.particularly in relation to FIG. 2.

FIG. 1 schematically illustrates the shape of the signals applied between the control electrodes of cells involved in the display, or display cells, (a) and of cells reserved for conditioning (b) and two possible variant forms of the latter having been given.

The signals are here represented in the form of a voltage V as a function of the time 2, this voltage being the potential difference between the two electrodes intercrossing over a cell and thus controlling it. They will,

for example, be applied in a conventional manner in the form of symmetrical half-voltages to the two control electrodes of a cell. They are constituted here by rectangular waveforms signals but could equally well have some other form, for example, sinusoidal or trapezoidal.

The holding signal S E is an alternating signal of periodicity T, and amplitude V permanently applied to the system of display cells. A writing signal 3,, consisting for example in an over-amplitude in the holding signal, sufficient to ionise the cells concerned, is applied to the cell or cells which are to be displayed. The problems of erasing are not dealt with here since in order to erase a written cell which is ionised twice per holding period T there is of course no need for conditioning.

The conditioning signals S in accordance with the invention are permanently applied to particular cells of the panel, reserved for the conditioning function, through the medium of corresponding electrodes. They have an amplitude 8, higher than or equal to S sufficient to ionise said conditioning cells. They may consist of a pulse of amplitude V applied to the conditioning cells with a frequency 11 times less than that of the holding signal; the conditioning cells are thenionised twice per cycle T nT They may equally be arranged to ionise only once per cycle T if the polarity of the applied signal only reverses with each cycle T In FIG. 1, the conditioning signal is constituted by two half-waves of a rectangular waveform signal of periodicity T repeated at a periodicity of T nT This results in two ionizations of the conditioning cells.

The ionization of the conditioning cells produces a light level much lower than that of the display cells which are regularly ionised 2n times per cycle T In the example shown in FIG. 1, where each cycle of the conditioning signal comprises two half-waves, the brilliance of the display cells is around n times greater than that of the conditioning cells.

The light emitted by the conditioning cells during ionisation, produced photoelectrons in the neighbouring cells and thus facilitates their writing. If the conditioning cells are suitably distributed within the panel, then the whole system will be conditioned.

To still further increase the speed of writing of a panel in accordance with the invention, and as the curves (b) and (c) of FIG. 1 show, the conditioning signals S, are supplemented by a signal, 4 or 8, identical to the conditioning signals S but applied synchronously with the writing signals The photoelectrons thus produced in the conditioning cells enable the neighbouring cells to ionise reliably as soon as the writing signal is applied. The two graphs (b) and (c) correspond to two possible variant embodiments, the signals S being applied respectively in phase opposition with the holding signals S or co-phasally therewith, the supplementary signal 4 or 8 in all cases being applied synchronously with the writing signal S,.

The result of this may be, depending upon whether the variant (b) or (c) is chosen, a differing level of ionization of the conditioning cell, as explained hereinafter in reference to FIG. 2.

In all cases, the ratio n between the frequency of the holding signal and that of the conditioning signal, is chosen sufficiently large for the contrast between the written and conditioned cells, to be good, this contrast being approximately equal to l/n. Experience has shown that values of n greater than l0or 20, produce good quality contrast.

On the other hand, n is made sufficiently small for the conditioning cells to light up without delay as soon as the conditioning signals are applied. Experience shows that for the gases generally used, a conditioning time of less than 2 ms is required.

For example, if theholding frequency is 50 kcs, a

value of n 50 produces excellent contrast and faultless lighting of the conditioning cells.

FIG. 2 illustrates in a highly schematic manner, part of a display panel P forming part of a display system in accordance with the invention. This panel P is entirely conventional in design and has not been described itself; embodiments of such panels are referred to in the aforementioned patent application.

In this figure, the periphery 20 of the panel, the control electrodes and certain of the cells, have been symbolically illustrated.

The electrodes are constituted by an intercrossing network of line electrodes EL EL EL EL EL represented in continuous line and column electrodes E E E E represented in broken line, to illustrate the fact that in relation to the line electrodes they are located on the other face of the panel P.

As already pointed out, the invention is applicable equally to a panel with a matrix or to a panel without a matrix. In either case, the gas cells are each located at the point where the control electrodes are crossing.

In this Figure, part of the control circuits for the panel P, has been shown, and in particular the circuits which are responsible for the conditioning function in accordance with the invention. The other circuits, and

in particular those for writing, erasing and addressing,

have not been shown, except insofar as their interaction with the conditioning circuits is concerned, their design being for the rest entirely conventional.

In the embodiment illustrated here which applies in particular to the display of alphanumerical characters, the panel P is divided into small rectangular display areas, s s for example, surrounded by frames reserved for conditioning. For this purpose, the network of elec-.

ditioning (electrodes E E E and E E for example).

The holding S and recording S, signals are applied, in the form of symmetrical half-levels for example, between the line and column electrodes of the display portions; the conditioning signals S are applied in the same manner, between the conditioning electrodes.

The display cells are represented by small circles, white for extinguished cells and black for illuminated cells which form a letter P in the surface s,.

The rest of the cells are reserved for conditioning; amongst these, certain ones have not been illustrated, being extinguished, and others have been marked by a black triangle, these ionising at the frequency l/T This is because the variant embodiment shown here corresponds to FIG. 1 (b) in which the conditioning signal S is applied in phase opposition with the holding signal S At the points of intercrossing of two conditioning electrodes, E and E for example, there appears between the electrodes a voltage V, Vc/ and Vc/ being respectively applied to these two electrodes), and the cells become ionized; but at the points of intercrossing between a conditioning electrode and a display electrode, E and E for example, the voltage is insufficient to ionize the cells (for example, V cl2)- The variant embodiment corresponding to FIG. 1 (0) could equally well be used. In this case, the whole of the cells controlled by the conditioning electrodes, could be ionised. This variant embodiment may be preferred, for example, in display systems where it is preferable to have larger elementary display areas and/or narrower neutralised bands for conditioning. In this case, the set of cells not used for display, is used for conditioning.

An example of conditioning control circuits in accordance with the invention has been schematically illustrated in said same FIG. 2.

A code converter element 21 receives at 22 the data which are to be displayed and supplies the different conventional control signals and addressing signals. lt controls a clock 23 the frequency H of which is, for example, that of the holding signals 8,; and which synchronises the whole control circuits. This clock 23, through shaper circuits which have not been shown,

generates the holding signals 8,; which are applied, through the medium of the blocks 24, 2S and the line and column interface circuits 26 and 27, respectively, between the electrodes reserved for display. The blocks 24 and 25 symbolise modulators transmitting the holding signal which they receive at E, in the absence of any writing data I, and a higher amplitude signal S, when they receive a data signal, the code converter element of course controlling the addressing of these data by the line and column selectors 26 and 27, respectively.

The conditioning signals S are for example generated in'the following manner. A frequency-divider 28 receives the clock signals 23 and produces signals of frequency H/n l/T which are supplied to a shaper element 29 producing conditioning signals 5, out of phase by in relation to the holding signals S E in the variant illustrated here. These signals, suitably amplified at 30 and 31, are applied in the form of symmetrical half-levels between the line and column electrodes reserved for the conditioning function. They are applied to the amplifiers 30 and 31 through the medium of adder circuits 32 and 33 of the OR-gate type, to whose first inputs they are applied. The second input of these OR-gates is supplied in each case with a supplementary conditioning signal which is said signal in synchronism with the writing signals 8,. For this purpose, a coincidence circuit 34, for example, and AND-gate, is supplied with signals at the frequency H of the clock 23, suitably shaped, and is open on a command from the code converter element 21 when writing takes place.

It should be noted that in all cases, the cells of the panel which are the closest those which are used for conditioning, have a higher probability of being quickly written. Thus it may be advantageous, in particular if the elementary display areas are relatively large, to repeat the writing signals several times in order to enable the cells to record step by step, each written cell providing the conditioning of its neighbours.

The supplementary conditioning signal applied during writing although producing supplementary ionization of the conditioning cells, produces no substantial degradation in the contrast because the sequences of recording are too short for the observer to be able to see the brief change in brilliance at the conditioning points.

It should also be pointed out that when a display system according to the invention starts to operate, the conditioning cells may not illuminate until after a few seconds as they are not themselves conditioned. This delay can be reduced by providing in these conditioning cells a small dose of a radioactive product, for Example, l micro-cutie of radium bromide.

What I claim is:

1. A display system with a gas discharge display panel, comprising a network of cells filled with gas ionisable on application of signals of appropriate amplitude between electrodes for controlling said cells, said control electrodes constituting a network of intercrossing electrodes disposed in lines and columns, means for applying an alternating holding signal of periodicity T between the control electrodes of the cells used for display, and producing, twice per cycle T the ionisation of written cells already ionized by tha application of a writing control signal, and means for conditioning the panel for providing within said panel some free electrons, said conditioning means comprising certain predetermined cells known as conditioning cells, distributed over the whole of the surface of the panel and being utilised only for said conditioning function, and means for providing conditioning signals of an amplitude high enough to provide ionisation of said conditioning cells between the electrodes controlling them at a frequency n times lower than the frequency UT, of said holding signal.

2. A display system as claimed claim 1, wherein the application of a writing signal between the control electrodes of display cells, controls the application, to the control electrodes of the conditioning cells, of a conditioning signal which ionises said conditioning cells as 8 soon as said writing signal is applied.

3. A display system as claimed in claim 2, wherein the conditioning signals are formed by a cycle T of an alternating signal, the frequency 1/ T of which is equal to that one of the holding signals, said cycle T recurring at a recurrence frequency l/T l/nT 4. A display system as claimed in claim 1 utilized for displaying alphanumerical characters, one character being displayed by a group of adjacent display cells, wherein said control electrodes are connected to sup- I ply means delivering said control and conditioning signals with said conditioning cells between and adjacent to said groups of display cells. 

1. A display system with a gas discharge display panel, comprising a network of cells filled with gas ionisable on application of signals of appropriate amplitude between electrodes for controlling said cells, said control electrodes constituting a network of intercrossing electrodes disposed in lines and columns, means for applying an alternating holding signal of periodicity T1 between the control electrodes of the cells used for display, and producing, twice per cycle T1, the ionisation of written cells already ionized by tha application of a writing control signal, and means for conditioning the panel for providing within said panel some free electrons, said conditioning means comprising certain predetermined cells known as conditioning cells, distributed over the whole of the surface of the panel and being utilised only for said conditioning function, and means for providing conditioning signals of an amplitude high enough to provide ionisation of said conditioning cells between the electrodes controlling them at a frequency n times lower than the frequency 1/T1 of said holding signal.
 2. A display system as claimed claim 1, wherein the application of a writing signal between the control electrodes of display cells, controls the application, to the control electrodes of the conditioning cells, of a conditioning signal which ionises said conditioning cells as soon as said writing signal is applied.
 3. A display system as claimed in claim 2, wherein the conditioning signals are formed by a cycle T1 of an alternating signal, the frequency 1/T1 of which is equal to that one of the holding signals, said cycle T1 recurring at a recurrence frequency 1/T2 1/nT1.
 4. A display system as claimed in claim 1 utilized for displaying alphanumerical characters, one character being displayed by a group of adjacent display cells, wherein said control electrodes are connected to supply means delivering said control and conditioning signals with said conditioning cells between and adjacent to said groups of display cells. 